●System register

• This is the memory for the system settings of the sprite IC, and is built into the VDP1 separately from the VRAM and frame buffer.

• There are read-only registers and write-only registers.

• Write-only registers are used to control frame buffer display. Select the TV mode, specify display switching and drawing triggers, and define the erase write fill data and area. You can also forcefully terminate drawing.

• Read-only registers are used as help information during program development. You can know the address of the command table that was last rendered and the address of the command table that is currently being processed.

• Be sure to perform read/write access from the CPU in word units.

• Do not use DMA burst transfers to access system registers.

• Except for the plot trigger register (PTMR), the values of write-only system registers become undefined after power-on or reset, so be sure to set the values using the CPU. The frame buffer will display indeterminate data until the appropriate value is set.

• Set unused bits of write-only system registers to 0.